Warning: Spoilers for My Hero Academia’s Final War arc
Summary
My Hero Academia’s big villain, All for One, is known for stealing the Quirks of others which he finds useful or interesting. However, there’s one truly fascinating Quirk which All for One never even learned about, much less had the chance to steal: Eri’s Rewind. It’s a good thing All for One never learned of this Quirk’s power, too, as it may have radically shifted things in his favor.
During the Shie Hassaikai arc, All for One is imprisoned in Tartarus, and is thus not aware of the activities going on outside involving the League of Villains. In fact, the League of Villains members actually never learn about Eri’s existence, either; while they know that Chisaki has these Quirk-deleting bullets, and they were later able to replicate some on their own, they seemingly had no knowledge of where the Quirk used in those bullets came from.

As a result, even Shigaraki and the League couldn’t have told All for One of Eri’s existence, and thus the tyrant never came to know what great power lay in the hands of this child.
Eri’s Quirk in All for One’s Hands Could’ve Changed Everything
Rewind’s Power Might Tip the Scales in the Villain’s Favor
If, hypothetically, All for One did learn about Eri’s Quirk, he likely would’ve made stealing it a priority. One of All for One’s big goals, after all, was to create himself a new body which was effectively immortal, and he needed to do this because his old body was in such bad shape after facing All Might.With Eri’s Quirk, All for One could simply rewind himself to a younger age, restoring his body to its physical prime and making it so that he wouldhardly even need Shigaraki.
During the Final War arc, All for One does use a serum derived from Eri’s Quirk to de-age himself, but he has no control over it, and it eventually rewinds him back to being a baby, and then out of existence entirely. If All for One had managed to get his hands on the original Quirk, Doctor Garaki could’ve studied it in depth, perhaps allowing him to develop a more precise serum which would grant the same de-aging effect without the risk of being erased from existence entirely. That alone would’ve radically altered the course of the final battle, without getting into Rewind’s potential offensive uses.
Thankfully, All for One never learned of Eri or her Quirk, except perhaps indirectly, as the source of his special serum. Eri has certainly had a hard enough life without having to deal with being a target of All for One, so being spared that fate was a fortunate turn of events for the child. It’s a bit odd to think that Eri’s Quirk could’ve had such a massive impact on the final battle, but given the power she wields, it’s far better that she was kept out of the fighting as much as possible.My Hero Academia’s ending could’ve been very different if All for One had learned of Eri, so fans should be glad she was kept safely out of sight.
My Hero Academia
My Hero Academia is a multimedia franchise that follows a young boy named Izuku Midoriya, who dreams of becoming a hero despite being born without superpowers. These superpowers, known as “Quirks” are found in most people after birth, but Izuku wasn’t so lucky - until a fateful encounter with All Might, Japan’s greatest hero, Izuku inherits his Quirk and enrolls in U.A. High School to learn the true meaning of heroism. Alongside his classmates, each endowed with unique abilities, Izuku faces rigorous training and lethal threats from villainous forces.